The influence of PPV chain aggregated structure on optical properties

A comparison has been made on the fluorescence of the poly (p-phenylenevinylene) (PPV) that without filtering the low molecular weight molecules (sample A) with the PPV of the low molecular weight molecules filtered (sample B). Although there is no obvious difference found in the FT-IR and Raman spectra between two samples, in the photoluminescence spectrum of the sample A, the peak at 510 nm is not appeared and the fluorescence intensity for the peak at 550 nm is increased. Under the high pressure condition the fluorescence peak at 520 nm, which corresponds to the peak at 510 nm of the usual PPV, is observed. Applying high pressure to the sample A or by filtering the low molecular weight molecules, the chain aggregated structure is modified, resulting in a change in the PPV chain distortion degree.     

Fluorogenic N,O-chelates built on a C2-symmetric aryleneethynylene platform: Spectroscopic and structural consequences of conformational preorganization and ligand denticity

Using π-extended aryleneethynylene as a rigid structural skeleton, a C₂-symmetric bis(picolinate) ligand was prepared. Binding of zinc(II) or cadmium(II) ion to this formally tetradentate N₂O₂-chelate resulted in significant red-shifts and enhancement in emission. The metal-ligand interaction responsible for such structural change was investigated by isolation and characterization of a tetrazinc(II) complex, in which the picolinate group functions not only as terminal bidentate but also as bridging with its μ-1,3 carboxylate unit.     

Isothermal titration calorimetric studies of the pH induced conformational changes of bovine serum albumin

Bovine serum albumin (BSA) is a soft globular protein that undergoes conformational changes through several identified transition steps in the pH range 2–13.5. The ability to change conformation makes BSA capable of complexing different ligands from fatty acids to cations or drugs and carries them in the bloodstream. Microcalorimetric titration of BSA with NaOH solution was performed to measure the enthalpy of conformational changes. Two exothermic enthalpy changes were found in the course of the titration between pH 3 and 9.5, which can be identified with the E–F, and the F–N transitions. The enthalpy change at pH 3.5 (transition from the E to the F form of BSA, folding of intra-domain helices in domain I) is independent of the protein concentration. The second transition (F–N, folding of domain III) was observed at pH 4.8 for the 0.1% BSA solution, but it shifted to higher pH values as the protein concentration increased to 0.2% and 0.3%. The tightening of the protein structure with increasing pH was verified measuring intrinsic fluorescence of tryptophan residues. At even higher pH value, pH 10.5, fluorescence measurements revealed protein expansion. The BSA conformational changes were also measured by dynamic light scattering. The hydrodynamic diameter was smaller at the i.e.p. of BSA (5–7 nm at pH ~5) and larger at the two ends of the pH range (17.5 nm at pH 2 and 8.3 nm at pH 10).     

Triphenylamine-based receptor for selective recognition of dicarboxylates

A new triphenylamine-based receptor 1 has been designed and synthesized for the recognition of aliphatic dicarboxylates of various chain lengths. This receptor has been designed to utilize an amide-urea conjugate for binding dicarboxylates. The receptor 1 is found to bind the dicarboxylates with moderate binding strength under a semi rigid, propeller shaped, fluorescent triphenylamine spacer. The binding behavior was studied in CH₃CN using ¹H NMR, fluorescence and UV-vis spectroscopic methods. The conformational behavior of 1 and its complexation modes have been investigated using classical and quantum mechanical theoretical methods. The receptor is found to be selective for long chain suberate.     

Rhodamine-conjugated acrylamide polymers exhibiting selective fluorescence enhancement at specific temperature ranges

A simple copolymer, poly(NIPAM-co-RD), consisting of N-isopropylacrylamide (NIPAM) and rhodamine (RD) units, behaves as a fluorescent temperature sensor exhibiting selective fluorescence enhancement at a specific temperature range (25–40 °C) in water. This is driven by a heat-induced phase transition of the polymer from coil to globule. At low temperature, the polymer exists as a polar coil state and shows very weak fluorescence. At >25 °C, the polymer weakly aggregates and forms a less polar domain within the polymer, leading to fluorescence enhancement. However, at >33 °C, strong polymer aggregation leads to a formation of huge polymer particles, which suppresses the incident light absorption by the RD units and shows very weak fluorescence. In the present work, effects of polymer concentration and type of acrylamide unit in the polymer have been investigated. The increase in the polymer concentration in water leads to a formation of less polar domain even at low temperature and, hence, widens the detectable temperature range to lower temperature. Addition of N-n-propylacrylamide (NNPAM) or N-isopropylmethacrylamide (NIPMAM) component to the polymer, which has lower or higher phase transition temperature than that of NIPAM, enables the aggregation temperature of the polymer to shift. This then shifts the detectable temperature region to lower or higher temperature.     

Photodissociative Modules that Control Dual-Emission Properties in Donor–π–Acceptor Organoborane Fluorophores

Donor–π–acceptor fluorophores that consist of an electron-donating amino group and an electron-accepting triarylborane moiety generally exhibit substantial solvatochromism in their fluorescence while retaining high fluorescence quantum yields even in polar media. Herein, we report a new family of this compound class, which bears ortho-P(=X)R₂-substituted phenyl groups (X=O or S) as a photodissociative module. The P=X moiety that intramolecularly coordinates to the boron atom undergoes dissociation in the excited state, giving rise to dual emission from the corresponding tetra- and tricoordinate boron species. The susceptibility of the systems to photodissociation depends on the coordination ability of the P=O and P=S moieties, whereby the latter facilitates dissociation. The intensity ratios of the dual emission bands are sensitive to environmental parameters, including temperature, solution polarity, and the viscosity of the medium. Moreover, precise tuning of the P(=X)R₂ group and the electron-donating amino moiety led to single-molecule white emission in solution.     

Temperature-dependent photoluminescence of water-soluble quantum dots for a bioprobe

The photoluminescence of water-soluble CdSe/ZnS core/shell quantum dots is found to be temperature-dependent: as temperature arising from 280 K to 351 K, the photoluminescence declines with emission peak shifting towards the red at a rate of ∼0.11 nm K⁻¹. And the studies show that the photoluminescence of water-soluble CdSe/ZnS quantum dots with core capped by a thinner ZnS shell is more sensitive to temperature than that of ones with core capped by a thicker one. That is, with 50% decrement of the quantum yield the temperature of the former need to arise from 280 K to 295 K, while the latter requires much higher temperature (315.6 K), which means that the integrality of shell coverage is a very important factor on temperature-sensitivity to for the photoluminescence of water-soluble CdSe/ZnS quantum dots. Moreover, it is found that the water-soluble CdSe quantum dots with different core sizes, whose cores are capped by thicker ZnS shells, possess almost the same sensitivity to the temperature. All of the studies about photoluminescence temperature-dependence of water-soluble CdSe/ZnS core/shell quantum dots show an indispensable proof for their applications in life science.     

Urea-induced Inactivation and Unfolding of Recombinant Phospholipid Hydroperoxide Glutathione Peroxidase from Oryza sativa

Phospholipid hydroperoxide glutathione peroxidase is an antioxidant enzyme that has the highest capability of reducing membrane-bound hydroperoxy lipids as compared to free organic and inorganic hydroperoxides amongst the glutathione peroxidases.In this study,urea-induced effects on the inactivation and unfolding of a recombinant phospholipid hydroperoxide glutathione peroxidase(PHGPx)from Oryza sativa were investigated by means of circular dichroism and fluorescence spectroscopy.With the increase of urea concentration,the residual activity of OsPHGPx decreases correspondingly.When the urea concentration is above 5.0 mol/L,there was no residual activity.In addition,the observed changes in intrinsic tryptophan fluorescence,the binding of the hydrophobic fluorescence probe ANS,and the far UV CD describe a common dependence on the concentration of urea suggesting that the conformational features of the native OsPHGPx are lost in a highly cooperative single transition.The unfolding process comprises of three zones:the native base-line zone between 0 and 2.5 mol/L urea,the transition zone between 2.5 and 5.5 mol/L urea,and the denatured base-line zone above 5.5 mol/L urea.The transition zone has a midpoint at about 4.0 mol/L urea.     

可溶性聚（2，5－二丁基氧基苯）薄膜荧光光谱的反常温度依赖特性

可溶性聚（２，５－二丁基氧基苯）薄膜荧光光谱的反常温度依赖特性马於光，吴英，张海峰，田文晶，沈家骢，刘式墉，孙猛（吉林大学分子光谱与分子结构开放实验室，集成光电子学国家实验室，长春，１３００２３）（复旦大学高分子科学系）关键词聚（２，５－二丁基氧基苯...     

Study of Imidazolium Ionic Liquids:Temperature-dependent Fluorescence and Molecular Dynamics Simulation

The steady-state fluorescence spectra and molecular dynamics simulations were explored to investigate the temperature dependent organization in some imidazolium ionic liquids:1-butyl-3-methylimidazolium hexafluo-rophosphate([bmim][PF6]),1-ethyl-3-methylimidazolium ethylsulfate([emim][EtSO4]) and 1-butyl-3-methylimida-zolium tetrafluoroborate([bmim][BF4]).The pure room temperature ionic liquids(ILs) exhibit a large red shift at more than an excitation wavelength of around 340 nm,which demonstrates the hetero...     

具有温度敏感和荧光特性的侧链查尔酮共聚物的研究

采用2,2′-偶氮二异丁腈作为引发剂,将N-异丙基丙烯酰胺和4-甲基丙烯酰氧基-4′-二甲氨基查尔酮单体,在四氢呋喃溶剂中通过自由基共聚制备了一系列具有溶剂和温度双重敏感荧光特性的侧链查尔酮共聚物,并通过红外光谱、核磁共振氢谱和紫外-可见光谱对其结构进行表征,通过吸光度法测定了共聚物中查尔酮单元的含量.研究了侧链查尔酮共聚物的温敏性以及溶剂极性和温度双重敏感的荧光特性.结果表明,侧链查尔酮共聚物是一类具有最低临界溶解温度（LCST）的温敏性聚合物,其LCST温度随着共聚物中查尔酮含量的增加而降低;随着溶剂极性的增加,侧链查尔酮共聚物的紫外-可见最大吸收波长红移,其荧光发光波长红移并且发光强度先增强后降低,具有溶剂极性敏感的荧光特性;同时对比侧链查尔酮共聚物水溶液低温和高温下的荧光,发现低温下几乎无荧光,高温下其荧光得到明显增强,其荧光具有可逆的温度“开/关”特性.     

Application of 3 μm particle-based amylose-derived chiral stationary phases for the enantioseparation of potential histone deacetylase inhibitors

In this work, we report on the difference in performance of the two 3 μm particle-based Chiralpak IA-3 and Chiralpak AD-3 chiral stationary phases (CSPs) in the direct resolution of four racemic cinnamyl 2-aminoanilides, endowed with histone deacetylase inhibitory activity. The 3 μm CSPs were explored to determine if they could provide an effective resolution of enantiomers in presence of alcoholic eluents such as pure methanol, ethanol and 2-propanol. Temperature variable enantioselective HPLC and subsequent van't Hoff analysis were performed. In most of cases the van't Hoff plots were found to show a non-linear behaviour. The knowledge of the enantiomeric elution order associated with the data coming from enantioselective HPLC permitted to advance some hypothesis about the groups involved in chiral recognition mechanism.